When information, such as voice or data, is received by a wireless communication device, such as a mobile station or a base transceiver station, the information is digitized, if not already in a digital format, and processed by one or more tasks performed by a respective processor of the communication device. The digitized data is then processed pursuant to a known protocol scheme.
A layered representation of protocols is commonly known as a protocol stack. A protocol stack commonly used for the interconnection of network systems is the TCP/IP Suite, named for two of the protocols, Transmission Control Protocol (TCP) and Internet Protocol (IP), in the stack. The TCP/IP protocol stack includes five layers, which layers are, from highest to lowest, an Application Layer, a Transport Layer, a Network Layer, a Link Layer, and a Physical Layer.
When the Link Layer, that is, Layer 2, functionality assembles a frame for transmission over a wireless link, the layer adds padding, typically a string of predetermined bits that convey no real information, such as a string of zeros (0's), to the frame if there is an insufficient amount of payload to fill out the frame. A result is that it is not unusual for a frame transmitted in a wireless communication system to contain a significant amount of padding. For example, reverse or forward link frames may contain as much as 20% to 50% padding, and more if header compression is used. More particularly, Radio Link Protocol (RLP)/Radio Link Control (RLC) control frames, particularly frames transmitted in a reverse link DCCH (Dedicated Control Channel), typically include more than 50% padding. For example, reverse and forward link RLP IDLE, NAK, and FILL frames constitute approximately 70% to 90% of the frames transferred and, typically, approximately the last 140 bits are padding, that is, all zeros. Other examples of reverse link messages that typically include significant padding are origination and page response messages (approximately 20% padding) and mobile station acknowledgements (approximately 90% padding).
Layer 2 functionality further implements protocols that assure a reliable transmission of data in a communication system that guarantees delivery of data. In order to assure a reliable transmission, Layer 2 may implement RLP/RLC or other automatic repeat request (ARQ) scheme to retransmit frames of data that were lost over the radio interface. A reliable Transport Layer protocol, such as TCP, may use RLP/RLC to guarantee that messages reach their destination complete and uncorrupted and in the order they were sent.
As is known in the art, wireless propagation of a frame may introduce errors to the data of the frame. When a reliable transport protocol is used and a receiving communication device is unable to correctly decode a received frame, a corresponding transmitting communication device retransmits the incorrectly received frame. For example, a receiving communication device that is unable to correctly decode a received frame may transmit a NAK to the transmitting communication device that identifies the erroneous frame. In response to receiving the NAK, the transmitting communication device retransmits the frame. By way of another example, a receiving communication device that is able to correctly decode a received frame may transmit an ACK to the transmitting communication device that identifies the correctly decoded frame. When a transmitting communication device fails to receive an ACK for a particular frame within a predetermined period of time, the transmitting communication device retransmits the frame.
A result is that frames that are erroneously received and that cannot be properly decoded are retransmitted, consuming valuable bandwidth and system capacity. However, when a transmitted frame includes significant padding, which contains no real information, errors that occur in the padding may cause a retransmission of the frame while being of no consequence to the information being conveyed.
Therefore a need exists for a method and an apparatus that minimizes a retransmission of erroneously received frames that include padding.